The scale of buttoning is one of the least discussed decisions in upholstery and one of the most visible. The distance between buttons determines how deep the folds are, how much shadow the surface holds, and - oddly - how large the whole piece looks. Small diamonds make a sofa read as bigger and busier, because the eye counts more units across the same width. Large diamonds make it read as calmer and, counter-intuitively, smaller.
Upholsterers used to work to whatever grid the horsehair needed to stay put, so the choice made itself. Now that fillings do not migrate, the grid is purely a design decision, and it should be made against the size of the room rather than copied from a catalogue photograph.
Our master Indian artisans set the grid out full size on the finished frame before any button goes in, so it can be judged against the actual length of your sofa rather than a drawing. On a long piece that is the only way to know whether the diamonds are the right size.